This invention relates to apparatus and methods for suspending, positioning, and manipulating objects by the use of acoustic energy.
Acoustic levitation of an object within a chamber has heretofore been accomplished by the use of one or a few acoustic standing wave patterns, wherein the acoustic wavelength was between about one-quarter and twice the length of the chamber. The chamber had to have highly sound reflective walls to provide a Q (a measure of sound reflectance) of at least about fifty. The object remained at a region of low acoustic pressure, because as it drifted in a particular direction, radiation pressure of the standing wave pattern pushed the object back. While harmonics of a fundamental or lowest frequency could be used, these higher harmonics restricted the size of the object. For these acoustic levitators, the object size had to be small compared to the acoustic wavelength, such as no more than about 20% of the wavelength. U.S. Pat. No. 4,573,356 describes the general state of the art of the use of acoustic standing wave patterns to levitate objects.
The prior art use of acoustic standing wave patterns, involved the use of one or only a few transducers which all emitted sound of relatively long wavelengths within a high Q chamber. A large sample requires a very long wavelength and long chamber. It is difficult to produce high intensity sound of long wavelengths and corresponding low frequencies. The force that could be applied to a levitated object was limited by the small number of transducers that could be easily used. Movement and shaping of the object required complicated control or required alteration of the chamber dimensions. A system for acoustically levitating an object, which enabled the effective application of acoustic energy from a large number of transducers, which avoided the need for a chamber of high Q, and which enabled simplified control of the position, shape, etc. of large objects with respect to the sound wavelength, would be of value.